Fluorine cell anode assembly



June 26, 1962 R. E. CABLE ET AL FLUORINE CELL ANODE ASSEMBLY Filed Aug.25, 1960 George H. Monfillon WQW ATTORNEY ttes This invention relates toelectrolytic cells and more particularly to electrolytic cells suitablefor the production of hydrogen and fluorine from a molten electrolytecomprising hydrogen fluoride absorbed in an alkali metal fluoride.

Hydrogen and fluorine gases may be produced in a suitable cell by theelectrolysis of an electrolyte comprising a mixture of hydrogen fluorideand an alkali metal fluoride.

The cell may comprise a plurality of cathodes and anodes immersed in theelectrolyte and thecell is constructed to collect the hydrogen andfluorine gases separately. Electrolytic cells for this purpose are wellknown in the art and one such cell is described in US. Patent No.2,544,285 to Kenneth E. Stuart and Sidney G. Osborne. The anodes ofcells of this character may comprise carbon which are at least partiallyimmersed in the electrolyte and which are held in position by a suitablemetal support above the surface of the electrolyte.

In electrolytic cells of this general character, considerable diificultyhas been experienced in the corrosion of the anode assembly by the fumesassociated with the operation of the cell. The carbon anodes arenormally clamped to a common metal hanger or bus bar by means of boltsand pressure plates. During operation of the cell, the corrosion, at themetal to carbon contact, builds up a high resistance deposit whichresults in a reduction of the power efliciency and of the life of thecell and eventually requires shutdown in the operation of the cell andexpensive overhauling of the anode assemblies. In addition, thecorrosion of the heads of the bolts, which fasten the carbon anodes tothe metal bus bar, will eventually cause the carbon anodes to loosenfrom the bus bar,

This arrangement has increased the cell life to 85x10 ampere-hours, ascompared to acell life of 16x10 ampere-hours for a conventional anodeassembly, and to a cell life of 32x10 ampere-hours when' larger, exposedclamping bolts were employed. 7

The single FIGURE 'in the drawing illustrates the manner in which thecarbon anodes are aflixed to a metal bus bar in accordance with theprinciples of'this invention. A common copper metal hanger or bus bar 1is supported by a metallic rod 7 which is affixed to bus bar 1 by anysuitable means. Rod 7 is provided with a reduced portion 8 and withscrew threads as shown in the drawing. The threaded portion of rod 7extends through an opening in the top of the electrolytric cell, notshown, and is employed in combination with a tap nut for securing therod 7 to the top of the cell. The portion 8 of the rod 7 is used forconnecting the rod 7 to a source of electrical power.

A plurality of two-inch thick carbon anodes 2 are affixed to the bus bar1 by means now to be described. Each of the anodes 2 has a plurality ofinch diameter holes drilled completely therethrough. Each of these holesis counter-bored to a depth of inch by a hole 1.384 inch in diameter,thus providing a shoulder or land for the head of a bolt 3. Each of thebolts 3 is inch by 2% inches with a slot-head. A 6 inch thick, copperwasher 4- is inserted under the head of each of the bolts 3 forprotection of the carbon anode. Each of the bolts 3 is provided withscrew-threads which engage the internal threads of a hold 6 in the busbar 1 for thus securing the anodes 2 to the bus bar 1, as clearly shownin the cut away portion of the drawing. Each of the bolts 3 is torquedto 120 ft. lbs. to produce an anode joint resistance of 49-65 microhmsas determined with a ductor low resistance ohmmeter. v

The head of each of bolts 3 is protected from corrosion by a 4 inchthick by 1.384 diameter carbon plug 5. These plugs 5 may be slightlytapered to insure a tight fit in the recessed holes in which they areinserted. As discussed above, an anode assembly provided with corrosionprotection plugs, as described above, has an average servresulting in alimited operation life for the cell due to failure of the cell at thispoint.

The cell life of the anode assembly may be materially increased byincreasing the size of the clamping bolts, but this has the disadvantageof materially increasing the corrosion products in the cell that couldcause internal electrical shorts. This would necessitate occasionaldeslndging to remove corrosion products so that maximum cell currentefficiency could be maintained.

With a knowledge of the factors which limited the cell life of prioranode assemblies, it is a primary object of this invention to provide anelectrolytic cell anode assembly in which corrosion of the assembly iskept to a minimum.

It is another object of this invention to provide an electrolytic cellanode assembly in which the quantity of corrosion products duringoperation of the cell is kept to a minimum.

It is still another object of this invention to provide an electrolyticcell anode assembly with a low anode joint resistance and with asubstantially long operating life.

These and other objects and advantages of this invention will becomeapparent upon a consideration of the following detailed specificationand the accompanying drawing wherein:

The single FIGURE illustrates one embodiment in which the principles ofthis invention may be carried out.

The above objects have been accomplished in the present invention byprotecting the clamping bolts from corrosion by placing them in recessedholes in the carbon anode and covering the heads of the bolts withcarbon plugs.

ice life of about x10 ampere-hours before failure of the assembly willoccur. This failure is caused by corrosion of the metal anode bus barwhich resulted in high contact resistance between the bar and thecarbon'anodes. This corrosion is attributed to a combination of thecorrosive action of active fluorine and electrolysis, particularly atsections of the bar experiencing high current densities.

The use of carbon plugs for protecting the clamping bolts willmaterially reduce the quantity of corrosion products formed duringoperation of the cell with the result that the cell will have to bedesludged only once before cell failure. An electrolytic cell in whichthe anode assembly of this invention is used has to be desludged atapproximately half life (45 10 ampere-hours) due to the corrosion of themetal bus bar and the cell tank.

It should now be apparent that the provision of means for protecting theclamping bolts of an anode assembly from corrosion during serviceoperation of the assembly in an electrolytic cell has effectivelyincreased the service life of the assembly and materially reduced thenumber of shutdowns required for desludging or overhauling of the anodeassembly.

This invention has been described by Way of illustration rather thanlimitation and it should be apparent that this invention is applicablein fields other than those decribed.

What is claimed is:

In a cell for generating fluorine, a long-lived anode assembly havingimproved corrosion resistance and low anode joint resistance, comprisinga copper post, a copper hanger connected to and supported by said post,a pluing the remaining members to the opposite side of said hanger, saidanode members depending from said hanger,

said clamping means including respective metal bolts and respectivecopper Washers under the heads of each of said bolts, said counterboredapertures each being provided with a shoulder for. the head and washerof each of said respective bolts and washers, said counterboresproviding respective recesses beyond the exterior ends of said bolts,said metal bolts extending through said apertures and into said hangerfor tightly clamping a portion of the Walls of said anode membersagainst said hanger, and shield members comprising carbon plugs insertedinto each of said recesses to protect said bolts from corrosion.

References Cited in the file of this patent UNITED STATES PATENTS

1. IN A CELL FOR GENERATING FLUORINE, A LONG-LIVED ANODE ASSEMBLY HAVINGIMPROVED CORROSION RESISTANCE AND LOW ANODE JOINT RESISTANCE, COMPRISINGA COPPER POST, A COOPER HANGER CONNECTED TO AND SUPPORTED BY SAID POST,A PLURALITY OF CARBON ANODE MEMBERS, EACH OF SAID ANODE MEMBERS PROVIDEDWITH A PLURALITY OF COUNTERBORED BOLT-RECEIVING APERTURES, MEANS FORCLAMPING A FIRST GRUP OF SAID ANODE MEMBERS TO ONE SIDE OF SAID HANGERAND FOR CLAMPING THE REMAINING MEMBERS TO THE OPPOSITE SIDE OF SAIDHANGER, SAID ANODE MEMBERS DEPENDING FROM SAID HANGER, SAID CLAMPINGMEANS INCLUDING RESPECTIVE METAL BOLTS AND RESPECTIVE COPPER WASHERSUNDER THE HEADS OF EACH OF SAID BOLTS, SAID COUNTERBOARD PERTURES EACHBEING PROVIDED WITH A SHOULDER FOR THE HEAD AND WASHER OF EACH OF SAIDRESPECTIVE BOLTS AND WASHERS OF EACH PROVIDING RESPECTIVE RECESSESBEYOUND THE EXTERIOR ENDS OF SAID BOLTS, SAID METAL BOLTS EXTENDINGTHROUGH SAID APERTURES AND INTO SAID HANGER FOR TIGHLY CLAMPING APORTION OF THE WALLS OF SAID ANODE MEMBERS AGAINST SAID HANGER, ANDSHIELD MEMBERS COMPRISING CARBON PLUGS INSERTED INTO EACH OF SAIDRECESSES TO PROTECT SAID BOLTS FROM CORROSION.